The present invention relates to a process for preparing an aerogel composed of inorganic oxides and comprising palladium, platinum, nickel, cobalt and/or copper; to homogeneously constructed, aerogel-supported transition metal catalysts produced in accordance with the process of the invention; and also to methods of using such catalysts.
Aerogel-supported metal catalysts are described by G. M. Pajonk in a review article in Appl. Catalysis, 72 (1991), pages 217 to 266. They are suitable for various purposes. Pt/SiO.sub.2 aerogel catalysts, for example, catalyze the oxidation of CH.sub.3 CHO to CH.sub.3 COOH. Ni/SiO.sub.2 aerogel catalysts catalyze the hydrogenation of toluene to methylcyclohexane. Cu/Al.sub.2 O.sub.3 aerogel catalysts catalyze the hydrogenation of cyclopentadiene to cyclopentene.
In Appl. Catalysis, 19 (1985), pages 339-348, the authors J. N. Armor, E. J. Carlson and P. M. Zambri describe the preparation of palladium/aluminum oxide aerogel-supported catalysts. These catalysts are suitable for the hydrogenation of nitrobenzene to aniline.
In Appl. Catalysis, 19 (1985), pages 327-337, the authors J. N. Armor and E. J. Carlson describe supported catalysts, namely palladium on aluminum oxide aerogel and also palladium on silicon dioxide aerogel in encapsulated form. Specific application purposes for these preparations are not indicated. However, from the context it appears that such preparations have a catalytic activity which is not more closely defined. In order to incorporate the palladium in the gel, a solution of palladium(II) acetate in warm acetone is prepared and mixed with the alkoxide precursors and an organic solvent. A problem here is that palladium(II) acetate is not readily soluble in alcohols. For this reason, in the preparation of the palladium aerogel-supported catalysts, inhomogeneous regions in the supported catalysts have to be expected.